The assembly of Human Immunodeficiency Virus-1 (HIV-1) is mediated by the Gag polyprotein. Located N- to C-term are the independently folded domains: matrix (MA), capsid (CA), and nucleocapsid(NC). Exposure of the N-terminal myristyl group of the HIV matrix protein is coupled with trimerization and further enhanced by the self-associating Gag subdomains. This targets the Gag polyprotein to lipid rafts in the plasma membrane during viral assembly. Evidence of the presence of the trimeric species has been demonstrated by analytical ultracentrifugation and X-ray crystallography of isolated proteins in solution, and by electron microscopic studies of Gag proteins assembled on lipid monolayers. Nuclear Magnetic Resonance (NMR) techniques will be used to study the protein-protein interactions involved at the matrix and capsid interfaces while in trimeric form. Knowledge of these interactions will provide a model of HIV-1 assembly and maturation thereby providing new therapeutic targets.